It is described in, e.g., the handbook.
It is known from the related art, e.g., the handbook Autoelektrik/Autoelektronik am Ottomotor/Bosch [Automotive Electrical and Electronic Systems on the Spark Ignition Engine/Bosch](1st edition, VDI Verlag 1987, ISBN 3-18-419 106-0), that the operation of an internal combustion engine should approach the knock limit as closely as possible for optimum torque. Knocking is an uncontrolled form of combustion which can damage an engine. For this reason, the firing angle is normally set so that there is always a safety margin from the knock limit. However, since the knock limit depends on fuel quality, engine condition and environmental conditions, gasoline consumption may be impaired due to the safety margin of late firing angles. Therefore, there have been many attempts to determine the knock limit during operation and set the firing angle as close to this known limit as possible. To guarantee operation as close to the knock limit as possible, knock sensors are provided to detect knocking and relay an appropriate signal to the control unit. One knock sensor is usually provided for multiple cylinders to detect knocking noises in these cylinders. In internal combustion engines with a large number of cylinders or with an unfavorable arrangement of cylinders, a knock sensor cannot sense all cylinders equally well due to the knock sensor installation site. In such cases, two knock sensors may be used per engine to permit analysis of sounds in all cylinders as much as possible.